Typically, the closing cap of the tube comprises a septum which can be passed through without difficulty by the sampling needle while providing a seal around the needle, and wherein the hole of passage of the needle closes in a sealed manner when the needle is extracted from the tube.
However, during the withdrawal of the needle, the friction of the needle in the hole of passage formed in the cap tends to raise the tube and to remove it from its means for support and positioning, with the risks of breakage of the tube and also risks of the loss of identification of the sample contained in the tube, when the means for identifying are borne by the support of the tube.
In order to avoid these disadvantages, it has already been proposed to provide such a sampling device with means for immobilising of the tube, which press against the periphery of the cap or on the upper end of the tube when the needle is descended through the cap and which then retain the tube and prevents it from raising again with the needle as long as the latter is not entirely withdrawn from the cap.
These known means include a ring or a part bearing on the cap, this ring or this part being mounted at the lower end of a rack which is guided in vertical translation in a bearing borne by a support element. The rack cooperates with a catch for immobilising and blocking which is solicited towards the rack by a spring mounted on the support element in such a way that the rack can descend into the bearing until the ring or the bearing part is placed on the cap or on the upper end of the tube, the rack then being blocked in this position by the catch which prevents it from rising back as long as the spring is not separated from the rack by a transversal finger which is mounted on the support of the needle and which accompanies the latter in its upward movement.
This known system of tube immobilisation has several disadvantages resulting substantially from the wear and tear of the catch on the teeth of the rack during the descent of the latter, risks of sliding of the catch on the teeth of the rack and of the vertical positioning by pitch of the rack in relation to its catch and to its support.